File: sed.info,  Node: Zero Address,  Prev: Range Addresses,  Up: sed addresses

4.5 Zero Address
================

As a GNU ‘sed’ extension, ‘0’ address can be used in these cases:
  1. In a regex range address as ‘0,/REGEXP/’ (*note Zero Address Regex
     Range::).
  2. With the ‘r’ command, inserting a file before the first line (*note
     Adding a header to multiple files::).
  3. As the starting address in the FIRST~STEP extension (*note Numeric
     Addresses::).

   Note that these are the only places where the ‘0’ address makes
sense; Commands which are given the ‘0’ address in any other way will
give an error.